'use strict';

var Eckles = require('eckles');
var Rasha = require('rasha');
var Enc = {};
var Keypairs = module.exports;

/*global Promise*/

Keypairs.generate = function (opts) {
  opts = opts || {};
  var kty = opts.kty || opts.type;
  if ('RSA' === kty) {
    return Rasha.generate(opts);
  }
  return Eckles.generate(opts);
};

Keypairs.import = function (opts) {
  return Eckles.import(opts.pem).catch(function () {
    return Rasha.import(opts.pem);
  });
};

Keypairs.export = function (opts) {
  return Promise.resolve().then(function () {
    if ('RSA' === opts.jwk.kty) {
      return Rasha.export(opts);
    } else {
      return Eckles.export(opts);
    }
  });
};

Keypairs.thumbprint = function (opts) {
  return Promise.resolve().then(function () {
    if ('RSA' === opts.jwk.kty) {
      return Rasha.thumbprint(opts);
    } else {
      return Eckles.thumbprint(opts);
    }
  });
};

// JWT a.k.a. JWS with Claims using Compact Serialization
Keypairs.signJwt = function (opts) {
  return Keypairs.thumbprint({ jwk: opts.jwk }).then(function (thumb) {
    var header = opts.header || {};
    var claims = JSON.parse(JSON.stringify(opts.claims || {}));
    header.typ = 'JWT';
    if (!header.kid) {
      header.kid = thumb;
    }
    if (false === claims.iat) {
      claims.iat = undefined;
    } else if (!claims.iat) {
      claims.iat = Math.round(Date.now()/1000);
    }
    if (false === claims.exp) {
      claims.exp = undefined;
    } else if (!claims.exp) {
      throw new Error("opts.claims.exp should be the expiration date (as seconds since the Unix epoch) or false");
    }
    if (false === claims.iss) {
      claims.iss = undefined;
    } else if (!claims.iss) {
      throw new Error("opts.claims.iss should be in the form of https://example.com/, a secure OIDC base url");
    }

    return Keypairs.signJws({
      jwk: opts.jwk
    , pem: opts.pem
    , protected: header
    , header: undefined
    , payload: claims
    }).then(function (jws) {
      return [ jws.protected, jws.payload, jws.signature ].join('.');
    });
  });
};

Keypairs.signJws = function (opts) {
  return Keypairs.thumbprint(opts).then(function (thumb) {

    function alg() {
      if (!opts.jwk) {
        throw new Error("opts.jwk must exist and must declare 'typ'");
      }
      return ('RSA' === opts.jwk.typ) ? "RS256" : "ES256";
    }

    function sign(pem) {
      var header = opts.header;
      var protect = opts.protected;
      var payload = opts.payload;

      // Compute JWS signature
      var protectedHeader = "";
      // Because unprotected headers are allowed, regrettably...
      // https://stackoverflow.com/a/46288694
      if (false !== protect) {
        if (!protect) { protect = {}; }
        if (!protect.alg) { protect.alg = alg(); }
        // There's a particular request where Let's Encrypt explicitly doesn't use a kid
        if (!protect.kid && false !== protect.kid) { protect.kid = thumb; }
        protectedHeader = JSON.stringify(protect);
      }

      // Convert payload to Buffer
      if ('string' !== typeof payload && !Buffer.isBuffer(payload)) {
        if (!payload) {
          throw new Error("opts.payload should be JSON, string, or Buffer (it may be empty, but that must be explicit)");
        }
        payload = JSON.stringify(payload);
      }
      if ('string' === typeof payload) {
        payload = Buffer.from(payload, 'binary');
      }

      // node specifies RSA-SHAxxx even whet it's actually ecdsa (it's all encoded x509 shasums anyway)
      var nodeAlg = "RSA-SHA" + (((protect||header).alg||'').replace(/^[^\d]+/, '')||'256');
      var protected64 = Enc.strToUrlBase64(protectedHeader);
      var payload64 = Enc.bufToUrlBase64(payload);
      var sig = require('crypto')
        .createSign(nodeAlg)
        .update(protect ? (protected64 + "." + payload64) : payload64)
        .sign(pem, 'base64')
        .replace(/\+/g, '-')
        .replace(/\//g, '_')
        .replace(/=/g, '')
      ;

      return {
        header: header
      , protected: protected64 || undefined
      , payload: payload64
      , signature: sig
      };
    }

    if (opts.pem && opts.jwk) {
      return sign(opts.pem);
    } else {
      return Keypairs.export({ jwk: opts.jwk }).then(sign);
    }
  });
};

Enc.strToUrlBase64 = function (str) {
  // node automatically can tell the difference
  // between uc2 (utf-8) strings and binary strings
  // so we don't have to re-encode the strings
  return Buffer.from(str).toString('base64')
    .replace(/\+/g, '-').replace(/\//g, '_').replace(/=/g, '');
};
Enc.bufToUrlBase64 = function (buf) {
  // allow for Uint8Array as a Buffer
  return Buffer.from(buf).toString('base64')
    .replace(/\+/g, '-').replace(/\//g, '_').replace(/=/g, '');
};